Anatase TiO2 was doped with metal ions like Th4+, V5+ and Mo6+ and tested for the degradation of imidachloprid under solar light. X-ray diffraction results inferred that all the dopants stabilized the anatase phase irrespective of their nature, oxidation state and ionic size. The undoped and transition metal ion doped TiO2 were completely transformed to rutile phase at 700 degrees C while rare earth Th4+ doped sample completely transformed to rutile phase at 1,000 degrees C. The rare earth dopant stabilized the anatase phase by hindering the growth of crystallite size. Among the photo catalysts used, Th4+ (0.06%)-TiO2 showed highest activity and its efficiency was 2.8 times higher than that of Degussa P-25. The Th4+ ion lowered the band gap of TiO2 to 2.6 and 2.5 eV facilitating solar light absorption. Detrapping of the trapped charge carriers depends on electronic configuration and the oxidation state of the dopants.